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Can fighting cats learn to live in harmony? (Proceedings)


A cat may become fearful, anxious or highly aroused in situations that are unpredictable, those that have been previously fear evoking, or when there is a perceived threat.

A cat may become fearful, anxious or highly aroused in situations that are unpredictable, those that have been previously fear evoking, or when there is a perceived threat. The cat's response can be to freeze and posture, attack, or flee. In addition, when there are competing motivations (conflict) or if the cat is frustrated from achieving its goal, the aggression may be redirected toward another individual who is more immediately accessible or is more vulnerable than the stimulus. Highly fearful or aroused cats can take hours to days to return to a normal baseline level.

Fear and anxiety in cats may arise as a result of genetics, inadequate early exposure, and unpleasant events or experiences. There may also be other factors influencing the pet's aggression including illness, pain and irritability, territorial behavior, and hierarchal relationships. When exposed to a fear evoking stimulus, the consequences of the pet's actions further aggravates the problem in that if aggression is successful at chasing away the threat it has been reinforced (negatively). On the other hand if the aggressive display leads to fear, retaliation or punishment, the pet's fear and aggression with each further exposure is likely to be heightened. Therefore, in order to successfully treat aggression, the pet's level of fear, anxiety or arousal will need to be reduced (e.g. with desensitization and or drugs) so that learning can occur.

Aggression can occur toward cats that live in the same household, especially new cats coming in to the territory. Cats recognize colony vs. non-colony members. In fact, aggression is typically exhibited by members of a cat "colony" toward unfamiliar cats that are not members of the colony. With persistence some cats may be integrated into an existing colony but this is a gradual process that takes many interactions. The same is likely to hold true therefore, when introducing a new cat into a household where one or more cats is already present. Another situation is when one cat is away from home (perhaps for routine surgery, boarding or being lost) and aggression is exhibited when the cat is brought back into the home. This aggression may be induced by fear or unfamiliarity (perhaps due to a change in odor, visual appearance or behavior).

In the wild, colony size is determined primarily by food resources which are, of course not likely to be an issue in a family home, if sufficient food and feeding stations are provided. However, within a home there are physical restrictions on space and dispersal. Therefore providing sufficient resources such as food, resting areas and litter boxes can help to insure a more harmonious relationship. If a cat is fearful of being disturbed when entering the litter box, housesoiling may arise. In addition, cats may attack others in the household that act fearful or more vulnerable. Since appeasement behaviors and postures are generally not part of the cats repertoire, when aggression begins there may be no way for it to naturally dissipate.

In a recent study of 128 households with multiple cats and 124 households with a single cat, about 50% reported fighting when a new cat was introduced into the home. Number of cats, age and sex were not associated with fighting. Ongoing fighting was associated with aggressive or unfriendly behavior by either the new or resident cat at the first meeting (e.g. scratching and biting), and outdoor access. In most cases it was the new cat that initially displayed fear or aggression, while the resident cat was more likely to try and initiate play.


Fear and aggression might be prevented or minimized if cats have received early socialization. Although cats may be born with the capacity to learn social skills, experience with their own and other species is necessary during early socialization (first 2 months). Therefore, adopting multiple cats of different ages or insuring contact with other cats during kittenhood and the juvenile period, can help prevent the cat from having dysfunctional relationships with other cats, which might include aggression, fear, and failure to understand intraspecific signaling. Kitten socialization classes are another option.

Introducing new cats into a household

When introducing a new cat into a household with existing cats, gradual familiarity should be established using scent, sound and then sight before allowing direct contact. This can most practically be accomplished by housing the new cat in a separate room and making all introductions gradual and positive. The correct time to begin cat-to-cat interactions can be highly variable. If both cats have had adequate socialization with other cats, and are not too timid or fearful, it may only be a matter of a few days to a few weeks before the cats are able to share the territory with little or no aggressive displays. Potential situations for aggression might also be managed by providing sufficient resources so as to reduce competition, sufficient three dimensional space so that cats might more easily avoid conflicts and time management so that cats can be separated at times when aggression might be displayed. Of course a veterinary visit should always be suggested for the new cat to insure that there are no potential health risks to the existing cats, and to help guide the owners through the introduction process. Even with graduated and positive introductions, in some homes aggression between cats may persist. In these cases, a lengthy separation is likely to be required in addition to a more formal desensitization and counter-conditioning program.

Treatment of fear aggression

A veterinary visit should be the starting point for each behavior case since diseases of virtually any organ system, cognitive dysfunction, pain, and sensory decline can cause or contribute to behavior problems. Once medical causes have been ruled out, a behavioral diagnosis and the cause(s) of the problem will need to be determined. The information required can be obtained from the history provided by the owner, videotape analysis of the problem (wherever possible) and observing and assessing the pet during the consultation (including the cat's response to stimuli). This information is also critical for developing a treatment plan that is specific to the pet and the household, as well as for determining the prognosis. A history form can be used for the initial history screening to review details of the problem, as well as to obtain background information about the family, home, schedule, and training and how it interacts socially with family, other pets and strangers. Unless you are providing a house call practice, it is also necessary for the client to provide a diagram of the home to determine its layout and to determine whether sufficient resources are provided including sleeping and perching areas, feeding sites, and litter boxes (locations, substrate, and maintenance) since these can all be a source of conflict.

History should then focus on the cats (signalment, personality, socialization, training, age obtained, etc); how they respond to stimuli; and how they interacts with family members, strangers and with each cat in the home. The owners and their lifestyle (24 hour schedule, training, play, etc) may also provide useful information. Finally the problem itself should be evaluated including how each of the cats get along, when the problem first arose, whether there are times when the cats groom or co-habitate without problems and a description (or preferably video) of when problems are likely to arise including what stimuli incite the aggression and each cat's response (i.e. aggressor or victim). Any treatment options already utilized should be discussed. .

The treatment program must be tailored to the individual pet and problem. Treatment advice would focus first on preventing recurrence to insure safety and prevent further aggravation of the problem. Modifications to the environment, behavior modification, behavior management products and medical therapy (see notes on drug therapy in pets) or surgery (e.g. neutering) might all be utilized.

Getting started – Preparing for exposure

Identifying all stimuli and situations in which aggression might arise is perhaps the most important information for prevention, determining the prognosis and developing a treatment (exposure) program. Exposure must begin with the stimulus (other cat) at low enough intensity that the pet does not display any fear, anxiety or aggression (desensitization) and to associated highly motivating rewards such as food treats with each exposure (counterconditioning). However, in practice it can be difficult to insure that the stimuli always remain sufficiently mild and to find a method for gradually increasing the intensity while avoiding fear or anxiety. Therefore before beginning any type of exposure exercises, the most practical method for graduated exposure will need to be determined. If the home has rooms that can be separated by a glass or screen partition or double height baby gates this might be a safe starting point. However, for direct introduction of cats even at a distance, the best way to insure success might be with the use of a leash and harness or wire mesh crate. Therefore before any exposure exercises these cats would need to first become accustomed to wearing the harness or being housed in the crate.

Another effective means of both controlling behavior and achieving a positive outcome when the cats are together is train the cats to respond to a few cue words or signals (such as shaking a box of treats). Some cats can be quite easily taught with lure reward or clicker training to exhibit a variety of behaviors on cue, which might then be used by the owner, to achieve desirable behaviors, before or as conflicts are about to arise.

Graduated exposure – desensitization and counterconditioning

When introducing or reintroducing two cats that are aggressive toward each other, the first step is to place the cats into separate rooms or parts of the home, thereby providing each cat with a separate territory. The goal of this step is for each cat to feel comfortable and secure in the home environment while being exposed to the sounds and smells of the other cat in an adjacent part of the home. In addition, this enforced separation avoids the possibility of threats, fearful displays, anxiety or aggression, which would further aggravate the problem. Insure that each territory provides a sufficiently enriched environment that provides opportunities for perching, climbing, bedding, scratching, elimination and play. When a new cat is being introduced into the home, the resident cat should be allowed access to the resources to which he or she is already accustomed and the new cat housed in a separate area with new litter, bedding, toys and perching areas. Separate housing arrangements should be kept stable for some time and moving forward will need to be based on closely monitoring the cats' responses.

Desensitization and counterconditioning could begin across a common doorway with each cat given highly motivating rewards such as food, treats or play toys. Stimulus intensity can be increased when there is no anxiety or apprehension about approaching and eating on opposite sides of the door. Fear and anxiety at any point in the program indicates that the owner is proceeding to quickly.

When the cats show no fear, anxiety, or threat toward each other behind closed doors, it may be useful to switch housing areas. In this way the cats are exposed to the other cat's odors and environment without direct exposure to the cats themselves. Monitor for fear and anxiety including appetite and urine marking. For those cats that are accustomed to being housed in cages, another option would be to place each cat in the other cats crate until it habituates and readily takes food or treats. Counter conditioning to the odor of the other cat(s) in the home might also be accomplished by grooming one of the cats with a brush or cotton cloth and then brushing the other cats with the same brush or cloth while giving favored food rewards.

The next phase is to move to visual contact. One option is to allow the cats to see each other through a glass or screen door while offering favored treats or play toys. Alternately it might be possible to use a door jam to open the door just enough for the cats to see or paw each other and to assess their responses while being fed. Once the cats have been calm on opposite sides of a door, reintroduction in a common area is the final goal.

To be successful the cats need to be far enough apart that they are relaxed and will take food or a treat (or favored play toy or catnip) while in the presence of the other cat. If favored rewards are saved exclusively for these introduction times, the cats may learn to expect "good things to happen" in the presence of each other (counter-conditioning). If the cats will not eat in each other's presence, for the next session the dishes will need to be moved farther apart and more appealing treats might be tried.

In some situations it may not be possible to find a sufficient distance where the cats will be interested in food or play and safety may also be an issue. In these cases the use of the leash and harness, crates or some highly effective training cues may be added to the program to achieve a positive outcome. Harnesses and crates might be used on one or both of the cats to maintain safe control while counterconditioning as well as to inhibit undesirable behavior (attack, retreat). Similarly favored rewards are used to maintain the cats focus and to reward desirable responses (no attack from the aggressor, no retreat from the victim). This is where clicker training can be particularly useful.

Allowing either cat to interact in an aggressive manner sets the program back. The cats must remain separated except during times such as feeding when the cats are distracted, occupied, and engaged in an enjoyable act. If the cats are doing well, you might want to increase their time together. Insure that they have sufficient space and resources so as to avoid conflicts. Try and determine if there are specific resources, areas of the home, times of the day, situations or even duration of time together where threats or aggression might occur, so that separation can be scheduled and planned before any problems are likely to begin.

Some cats may never become compatible housemates. Although cats do live in social groups, they also have the opportunity to leave them. The social groups we create in the home do not provide that opportunity. The only way to avoid fighting in these cats may be to find a new home for one of the cats, or to provide separate living quarters for each cat within the home.

Immediate intervention

Even if the program is successful and progress is made, there may be unexpected times when aggression recurs the issue of how to safely address the situation arises. It might be possible to distract or reorient the cats with a favored toy or treat, a previously trained cue or signal (e.g. come, shaking a treat jar) or by pulling on the leash and harness, if one has been left attached. Alternately throwing a large blanket or comforter over the aggressor and removing it into a dark quiet room until it calms may be the only safe approach.

Drug therapy

In general drugs that reduce fear and anxiety may help one or both of the cats. However, treatment strategies could focus on reducing the attacks and impulsivity of the aggressor cat with drugs such as the selective serotonin reuptake inhibitors or tricyclic antidepressants, while the confidence of the fearful cat might be increased by antidepressants, buspirone or benzodiazepines such as oxazepam, which might also improve appetite for counterconditioning. Also see notes on drug therapy.


1. Crowell-Davis SL, Curtis TM, Knowles RJ. Social organization in the cat: a modern understanding. J Fel Med Surg 2004;6,19-28

2. Wolfe R. The social organization of the free ranging domestic cat (Felis catus). PhD dissertation, 2001, University of Georgia

3. Levine E, Perry P, Scarlett J, Houpt KA. Intercat aggression in households following the introduction of a new cat. Appl Anim Behav Sci 2005: 90, 325-336

Additional reading and references

Horwitz D. Landsberg GM. Client Behavior Handouts on line, Lifelearn, Lifelearncliented.com, 2009

Landsberg G, Hunthausen W, Ackerman L. Handbook of Behavior Problems of the Dog and Cat, 2nd edition, Saunders, Edinburgh, 2003

Horwitz D, Neilson J. Blackwell's Five Minute Veterinary Consult Clinical Companion Canine & Feline Behavior, Blackwell, 2007

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